How strong would a civ with a mounted villager be?

Hypothetically, how strong do you think a civ with the following characteristics would be:

• Average tech tree (units/BS upgrades/eco upgrades)
• Unique unit: Mounted villager. Functionally identical to a villager, but with the speed of a missionary. Has 'cavalry' armor class. Built from TC and castle for 75 food.
• Imp-age unique tech: Mounted villagers lose detrimental effects of 'cavalry' armor class, keep beneficial effects.
• Other bonuses, castle-age unique tech: average